Isosteric heats of adsorption for nitrogen adsorbed on microporous silica

Abstract

Nitrogen adsorption isotherms at three different but similar temperatures were determined on samples of microporous silicas prepared by a freeze–thaw technique. A maximum in the plot of the isosteric heat of adsorption against coverage was observed on all the samples investigated. It is suggested that the effect can be explained in terms of lateral interaction between adsorbate molecules being important in the narrowest pores whilst in the larger micropores surface heterogeneity may play a predominant role. The microporosity of the silicas is established by adsorbing adsorbates of different molecular size and noting the adsorption capacity at a relative pressure near saturation.